title: Soil denitrification potential and its influence on N2O reduction and N2O isotopomer ratios.
abstract: BACKGROUND
  N2O isotopomer ratios may provide a useful tool for studying N2O source processes in soils and may also help estimating N2O reduction to N2. However, remaining uncertainties about different processes and their characteristic isotope effects still hamper its application. We conducted two laboratory incubation experiments (i) to compare the denitrification potential and N2O/(N2O+N2) product ratio of denitrification of various soil types from Northern Germany, and (ii) to investigate the effect of N2O reduction on the intramolecular (15)N distribution of emitted N2O.
  
  
  METHODS
  Three contrasting soils (clay, loamy, and sandy soil) were amended with nitrate solution and incubated under N2 -free He atmosphere in a fully automated incubation system over 9 or 28 days in two experiments. N2O, N2, and CO2 release was quantified by online gas chromatography. In addition, the N2O isotopomer ratios were determined by isotope-ratio mass spectrometry (IRMS) and the net enrichment factors of the (15)N site preference (SP) of the N2O-to-N2 reduction step (η(SP)) were estimated using a Rayleigh model.
  
  
  RESULTS
  The total denitrification rate was highest in clay soil and lowest in sandy soil. Surprisingly, the N2O/(N2O+N2) product ratio in clay and loam soil was identical; however, it was significantly lower in sandy soil. The IRMS measurements revealed highest N2O SP values in clay soil and lowest SP values in sandy soil. The η(SP) values of N2O reduction were between -8.2 and -6.1‰, and a significant relationship between δ(18)O and SP values was found.
  
  
  CONCLUSIONS
  Both experiments showed that the N2O/(N2O+N2) product ratio of denitrification is not solely controlled by the available carbon content of the soil or by the denitrification rate. Differences in N2O SP values could not be explained by variations in N2O reduction between soils, but rather originate from other processes involved in denitrification. The linear δ(18)O vs SP relationship may be indicative for N2O reduction; however, it deviates significantly from the findings of previous studies.
authors.affiliation: Institute of Plant Nutrition and Soil Science, Kiel University, Hermann-Rodewald-Str. 2, D-24118, Kiel, Germany.
authors.forename: Jan Reent
authors.initials: JR
authors.lastname: Köster
authors.forename: Reinhard
authors.initials: R
authors.lastname: Well
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittert
authors.forename: Anette
authors.initials: A
authors.lastname: Giesemann
authors.forename: Dominika
authors.initials: D
authors.lastname: Lewicka-Szczebak
authors.forename: Karl-Hermann
authors.initials: KH
authors.lastname: Mühling
authors.forename: Antje
authors.initials: A
authors.lastname: Herrmann
authors.forename: Joachim
authors.initials: J
authors.lastname: Lammel
authors.forename: Mehmet
authors.initials: M
authors.lastname: Senbayram
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D002245:Carbon Dioxide / Q000032:analysis; D000077215:Clay; D058440:Denitrification; D005740:Gases / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis; D009587:Nitrogen Isotopes / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis*; D010084:Oxidation-Reduction; D012822:Silicon Dioxide / Q000737:chemistry; D012987:Soil / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D005740:Gases; D009587:Nitrogen Isotopes; D012987:Soil; D002245:Carbon Dioxide; D012822:Silicon Dioxide; D009609:Nitrous Oxide; D009584:Nitrogen; D000077215:Clay